The present invention relates to a vehicle suspension system which ensures a suitable vehicle inclination matching the track curvature so as to counterbalance the centrifugal force acting upon the floor bearing level of the vehicle.
It is applicable to railway vehicles, more particularly to so-called articulated trains in which the coupling between vehicles prevents relative lateral movements and in which the running gear and suspension components are located within the free space between vehicles.
It is well known that one of the factors limiting the speed of trains on curves is the maximum permissible acceleration in a lateral direction, to which passengers can be subjected within the bounds of comfort.
Part of the centrifugal acceleration is counteracted by grading the roadbed of the track, that is the cant at the curves, so that passengers are only subjected to the centrifugal acceleration in the vehicle plane.
Nevertheless, since the extent of cant has to be limited to a maximum value to allow sharing of the tracks by both fast and slow trains and to allow for possible stopping on a curve, the cant alone tends to be insufficient, particularly in the case of fast trains run on tracks with limited radius of curvature. This is particularly important in areas or countries with an irregular topography.
In addition to the insufficient cant, there is unfavourable effect of the vehicle sloping towards the outside of the curve in the event the suspension being distorsed because of its normal location on a plane considerably below the centre of gravity of the suspended mass.
This tilt is greater than might be assumed on first impression, and is an inherent characteristic of each vehicle. It is defined as a coefficient representing the ratio, between the angle formed by the body in relation to the track when the train is stationary on the track, and the relevant angle of cant. In the case of conventional trains, the normal value of the coefficient is 0.4 which means that 40% of the favourable effect of the cant is lost, when running on a track with an insufficient cant of the same magnitude as the relevant cant.
A procedure for achieving total compensation for the centrifugal force from a passenger viewpoint, consists in producing a pendular oscillation of the coaches, the longitudinal axis of rotation being located above the centre of gravity. Such purely pendular vehicles, which have not gone beyond the experimental stage, have a number of disadvantages, of which the most important is the lack of stability against rolling as the use of shock-absorbers to correct this defect will only serve to delay the tilting of the vehicle upon entering a curve.
Other known apparatus employ artificial automatic control arrangements with centrifugal or other types of controls, installed to detect the curve and transmit a signal to servo-controls which ensure the tilting of the coaches. In spite of the obvious advantages, they all suffer from delayed tilting on entering curves, due to the time required to ascertain that the vehicle is in fact approaching a curve and that the signal is not produced simply by accidental movement of the vehicle, and also due to the time required to produce the actual tilting.
As a solution of the problem, the installation of a programmed computer in the vehicle, following the track characteristics, has also been tried. However, this manner of solution raises the cost even further.